1. Field of the invention
The present invention relates to a novel capillary column for capillary electrophoresis. More particularly, it relates to a capillary column which employs a packing material for capillary electrophoresis which can be easily packed into a capillary, can form a homogeneous gel in the capillary, shows no damage on the formed gel by formation of bubbles and the like, thus, can be utilized with stability and is favorably utilized for separation and analysis of proteins, nucleic acids, amino acids and the like.
2. Description of the prior art
Electrophoresis has been utilized for the analysis of proteins, nucleic acids, decomposition products thereof and other like various substances. The electrophoresis comprises various methods, such as gel electrophoresis, filter paper electrophoresis, isoelectric point electrophoresis and the like. Because a gel generally prevents occurrence of convection and protects the sample from adverse effects of reactions such as generation of gas at the electrode, it is a favorable medium for fractionating proteins and nucleic acids and the like to narrow bands.
Capillary electrophoresis is a method of gel electrophoresis preformed in a gel packed in a capillary. As the gel for this method, polyacrylamide gel which does not show electroosmosis is generally utilized.
Recently, a method of utilizing agarose which is a natural polysaccharide as the gel for the capillary was proposed (Journal of Chromatography, Volume 458, Pages 303-312 (1988)). A method of utilizing Curdlan.RTM. which is a .beta.-glucan as a gel for the electrophoresis was also proposed (Analytical Sciences, Volume 7, Pages 811-812 (October 1991)).
However, polyacrylamide gel has problems: (1) bubbles tend to be formed by contraction of volume during the preparation of gel (polymerization) and unfavorable phenomena frequently take place, such as damage of the gel by the formation of bubbles during the preparation of the gel or during the operation of the electrophoresis; (2) the operation of packing the packing material into the capillary is complicated and requires skill; (3) because unstable crosslinking agents must be utilized, preparation of homogeneous gel is not easy and the operation must be completed in a short time; and (4) because acrylamide reportedly has an adverse effect on health, care must be taken to avoid an adverse effect on health.
The method of utilizing agarose as the gel for the capillary has the fatal problem that agarose is mechanically weak and flows out of the capillary during the electrophoresis. Furthermore, the gel formed by agarose becomes heated during the operation of the electrophoresis and the rise of temperature causes melting of the gel. This is another cause of the flowing out of the capillary. Thus, a sample mixture cannot be separated with good reproducibility by the electrophoresis utilizing the capillary column (namely gel-filled capillary) packed with agarose gel.
According to the published method of utilizing curdlan as the gel, a column of 3.5 nun diameter was used. The column of this size cannot be regarded as a capillary column. Also, the molecular weight of Curdlan.RTM. is so low (at most 100,000) that it is required to pack Curdlan.RTM. into a column at high concentration like 15 weight % as described in the above mentioned journal in order to use it as the separation column. It is very difficult to pack the material of such a high concentration into an ordinary capillary whose diameter is generally less than 1 mm. Furthermore, in a column of this concentration, high molecular weight components like proteins or nucleic acids cannot be separated even though low molecular weight components may be separated.